JP2013133284A - Method for producing epsilon-caprolactam - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing ε-caprolactam, by which the ε-caprolactam having high quality and having reduced impurities can be produced from crude ε-caprolactam containing impurities in a good yield with saved energy.SOLUTION: The method for producing the ε-caprolactam includes a first process for evaporating an organic solvent from a solution prepared by dissolving crude ε-caprolactam obtained by the Beckmann's rearrangement of cyclohexanone oxime in the organic solvent under reduced pressure to crystallize the ε-caprolactam, and then subjecting the crystallized ε-caprolactam to a solid-liquid separation from the solution, and a second process for further crystallizing the ε-caprolactam from the liquid phase obtained by the solid-liquid separation and then subjecting the crystallized ε-caprolactam to a solid-liquid separation from the liquid phase.

Description

  The present invention relates to a method for producing ε-caprolactam, and in particular, to a method for producing high-quality ε-caprolactam with high yield by crystallizing crude ε-caprolactam containing impurities obtained by Beckmann rearrangement of cyclohexanone oxime. .

 ε-Caprolactam is an important compound as a production intermediate of nylon-6, and various production methods are known. For example, it is produced in large quantities by subjecting cyclohexanone oxime to Beckmann rearrangement in the presence of an acidic medium such as fuming sulfuric acid. However, this method has a problem that a large amount of ammonium sulfate with a small added value is by-produced.

  As a method for improving this, a method for producing ε-caprolactam by a gas phase Beckmann rearrangement reaction using a solid catalyst is known. As the solid catalyst used in the gas phase Beckmann rearrangement reaction, a boric acid catalyst, a silica / alumina catalyst, a solid phosphoric acid catalyst, a composite metal oxide catalyst, a zeolite catalyst, and the like have been proposed. However, since ε-caprolactam obtained by this method contains various impurities, it is usually purified by various methods such as crystallization, extraction, distillation and hydrogenation.

  Among these purification methods, the crystallization method is known in terms of energy as compared with the distillation method and the like, and is a method that can remove relatively many impurities at a time. As the crystallization method, a cooling crystallization method in which a liquid to be separated is cooled to precipitate a crystal, an evaporation crystallization method in which a crystal is precipitated by evaporating and removing a solvent in the liquid to be separated, and a separation target. A poor solvent crystallization method in which the solubility of the target product is lowered by adding a poor solvent to the liquid to precipitate the crystal, and a crystallizing by various methods is performed, and then the temperature of the crystal is raised to remove the impurities. Laws are frequently used industrially.

  Patent Document 1 discloses a method for producing purified ε-caprolactam by solid-liquid separation by crystallizing ε-caprolactam by co-mixing a molten crude ε-caprolactam and a cooled organic solvent. It is disclosed.

JP 2002-3472 A

  In the case of producing purified ε-caprolactam using the above-described crystallization method, it is necessary to operate a large refrigerator to cool the organic solvent, which consumes a lot of energy. For this reason, in recent years when energy saving during production is an important examination item, a production method capable of producing high-quality ε-caprolactam with low energy consumption has been demanded.

  The present invention has been made in view of such circumstances, and it is possible to reduce impurities with low energy consumption from crude ε-caprolactam containing impurities, and to produce ε-caprolactam with high yield in high yield. An object is to provide a manufacturing method.

  In order to solve the above problems, the present invention crystallizes ε-caprolactam by evaporating the organic solvent under reduced pressure from a solution obtained by dissolving crude ε-caprolactam obtained by Beckmann rearrangement of cyclohexanone oxime in an organic solvent. Then, the first step of solid-liquid separation of the crystallized ε-caprolactam from the solution, and ε-caprolactam further crystallized from the liquid phase obtained by solid-liquid separation, and the crystallized ε-caprolactam is obtained. And a second step of solid-liquid separation from the liquid phase.

  In the present invention, the solvent is evaporated from the crude ε-caprolactam solution to crystallize ε-caprolactam, and ε-caprolactam is obtained by solid-liquid separation that follows. That is, in the crystallization operation, by using the latent heat of evaporation of the solution of ε-caprolactam, cooling crystallization under reduced pressure (evaporation crystallization) is used to cool the crystallization tank using a refrigerator or the like and cool the entire solution. Thus, it is possible to reduce the amount of energy required as compared with the crystallization method.

  In the method of cooling the crystallization tank, scaling may occur on the heat transfer surface of the crystallization tank, but such scaling is suppressed in the evaporation crystallization. As a result, high-quality ε-caprolactam is stably obtained.

  Furthermore, from the liquid phase obtained by solid-liquid separation, ε-caprolactam is crystallized by various methods to recover ε-caprolactam, thereby increasing the recovery rate.

  From the above, in the method for producing ε-caprolactam of the present invention, impurities can be reduced from crude ε-caprolactam containing impurities with low energy consumption, and high-quality ε-caprolactam can be produced in high yield. It becomes possible.

  In the present invention, it is desirable to circulate and use at least a part of the organic solvent evaporated from the solution as an organic solvent for dissolving the crude ε-caprolactam.

  In the present invention, it is desirable to circulate and use ε-caprolactam obtained by solid-liquid separation in the second step as a crystallization raw material in the first step.

  In the present invention, an organic solvent is recovered from the liquid phase obtained by solid-liquid separation in the second step, and at least a part of the recovered organic solvent is circulated as an organic solvent for dissolving the crude ε-caprolactam. It is desirable to use it.

  In the present invention, it is desirable to wash ε-caprolactam obtained by solid-liquid separation with an organic solvent in at least one of the first step and the second step.

  In the present invention, it is desirable to continuously perform crystallization and solid-liquid separation in at least one of the first step and the second step.

  In the present invention, the organic solvent for dissolving the crude ε-caprolactam may be an aliphatic hydrocarbon solvent or a mixed solvent of an aliphatic hydrocarbon and a small amount of an organic solvent having a polarity higher than that of the aliphatic hydrocarbon. desirable.

  In the present invention, the aliphatic hydrocarbon solvent is preferably at least one of aliphatic straight chain hydrocarbons, aliphatic side chain hydrocarbons, and alicyclic hydrocarbons having 6 to 12 carbon atoms.

  In the present invention, the aliphatic hydrocarbon solvent is preferably a mixed solvent of an aliphatic linear hydrocarbon and an alicyclic hydrocarbon.

  In the present invention, the crude ε-caprolactam is desirably obtained by gas phase Beckmann rearrangement of cyclohexanone oxime in the presence of a solid catalyst.

  In the present invention, in the first step, it is desirable that ε-caprolactam obtained by solid-liquid separation after crystallization treatment is then brought into contact with hydrogen in the presence of a hydrogenation catalyst.

  In the present invention, the concentration of cyclohexanone oxime contained in crude ε-caprolactam is 10 ppm or more with respect to ε-caprolactam, and the concentration of 1,2,3,4,6,7,8,9-octahydrophenazine. 10 ppm or more with respect to ε-caprolactam, the concentration of 3-N-methyl-4,5,6,7-tetrahydrobenzimidazole is 25 ppm or more with respect to ε-caprolactam and the concentration of caprenolactams with respect to ε-caprolactam It is desirable that it is 25 ppm or more.

  In the production method of ε-caprolactam of the present invention, impurities can be reduced from crude ε-caprolactam containing impurities with low energy consumption, and high-quality ε-caprolactam can be produced with good yield.

It is a figure which shows the process process of the manufacturing method of the epsilon caprolactam which concerns on this invention.

  In the production method of ε-caprolactam according to the present embodiment, ε-caprolactam crystallized after evaporating the organic solvent under reduced pressure to crystallize ε-caprolactam from a solution obtained by dissolving crude ε-caprolactam in an organic solvent. A first step of solid-liquid separation from the solution, and a second step of further crystallization of the liquid phase obtained by solid-liquid separation and solid-liquid separation of the crystallized ε-caprolactam from the liquid phase. Have.

  In the present specification, “crude ε-caprolactam” means ε-caprolactam which is a target product obtained in the production process of ε-caprolactam, and impurities (reaction solvent, unreacted raw materials, side reaction products, etc.) And a reaction mixture. The following explanation was obtained by gas phase Beckmann rearrangement using a zeolite catalyst such as silica-alumina, metallosilicate, silicalite, etc. as crude ε-caprolactam (hereinafter sometimes abbreviated as “crude lactam”). Although the reaction mixture is exemplified, the crude lactam to which the present invention can be applied is not limited thereto.

FIG. 1 is a flowchart when the manufacturing method of the present embodiment is carried out in a continuous process.
The steps described in the figure include a dissolution tank 1 for dissolving crude lactam in an organic solvent, a crystallization tank 2 for crystallizing ε-caprolactam from a solution in which the crude lactam is dissolved, and an organic solvent that evaporates in the crystallization tank 2 is concentrated. A condenser 3 for liquefaction, a solid-liquid separator 4 for separating the crystals of ε-caprolactam deposited in the crystallization tank 2, a crystal washer 5 for washing the separated crystals of ε-caprolactam, a solid-liquid separator 4 and A crystallization tank 6 for further crystallization from the liquid phase generated in the crystal washer 5, and a solid-liquid separator 7 for separating ε-caprolactam crystals precipitated in the crystallization tank 6 from the solution are included.

In the figure, a process using the dissolution tank 1, the crystallization tank 2, the condenser 3, the solid-liquid separator 4 and the crystal washing machine 5 corresponds to the “first process” in the present invention, and the crystallization tank 6, the solid-liquid separation. The process using the machine 7 corresponds to the “second process” in the present invention.
Hereinafter, it demonstrates in order.

(First step)
First, the crude lactam is dissolved in an organic solvent in the dissolution tank 1.
The crude lactam is not uniquely defined depending on the production method, but in addition to methanol and unreacted cyclohexanone oxime used as a solvent, cyclohexanone, cyclohexenone, n-hexonitrile, 5-hexonitrile, methyl lactam, 1,3,4, 5-tetrahydroazepin-2-one, 1,5,6,7-tetrahydroazepin-2-one, 1,2,3,4,6,7,8,9-octahydrophenazine (hereinafter abbreviated as OHP) And various by-products such as amines such as 3-N-methyl-4,5,6,7-tetrahydrobenzimidazole (hereinafter abbreviated as MTHI).

  For example, in the crude lactam obtained by the gas phase Beckmann rearrangement method, the concentration of cyclohexanone oxime is usually 10 ppm or more with respect to ε-caprolactam, 1,2,3,4,6,7,8,9-octa. The concentration of hydrophenazine is 10 ppm or more, the concentration of 3-N-methyl-4,5,6,7-tetrahydrobenzimidazole is 25 ppm or more, and 1,3,4,5-tetrahydroazepin-2-one, The concentration of 6,7-tetrahydroazepin-2-one and their structural isomers (hereinafter abbreviated as caprenolactams) is contained at 25 ppm or more. Among these impurities, caprenolactams are included. Except for this, it is possible to remove and purify all at once by applying the crystallization method of the present invention.

  The crude lactam obtained by the gas phase Beckmann rearrangement reaction using a zeolite-based catalyst contains a solvent such as methanol, various low-boiling by-products, and various high-boiling by-products. Therefore, for the purpose of increasing the crystallization efficiency, it is preferable to carry out preliminary distillation or the like to remove some or all of these solvents and by-products as necessary before dissolution in the dissolution tank 1.

  As the organic solvent used in the dissolution tank 1, an aliphatic hydrocarbon solvent having a low polarity is recommended so that a large amount of lactam does not remain in the solution after crystallization.

  Examples of such aliphatic hydrocarbon solvents include aliphatic straight chain hydrocarbons having 6 to 12 carbon atoms, aliphatic side chain hydrocarbons, and alicyclic hydrocarbons. More specifically, aliphatic side chain hydrocarbons such as n-hexane, n-heptane, n-octane, n-nonane, n-decane, etc., aliphatic hexanes such as methylhexane, isooctane, neohexane, Examples thereof include alicyclic hydrocarbons such as methylcyclopentane, cyclohexane, and methylcyclohexane, and mixtures of aliphatic hydrocarbons such as petroleum benzine (specified in JIS K 8594. Mixtures such as hexane and isohexane). Among them, aliphatic hydrocarbons having a boiling point not lower than the melting point (69 ° C.) of ε-caprolactam and lower than the boiling point of ε-caprolactam (267 ° C.), such as n-heptane, isooctane, and petroleum benzine, are preferable, and the boiling point is ε-caprolactam. An aliphatic hydrocarbon (for example, cyclohexane, etc.) having a melting point or higher and about 150 ° C. or lower is more preferable.

  These may be used alone or in combination of two or more or more polar organic solvents that can be mixed uniformly with these. That is, as long as impurities that are the object of the present invention can be removed, a small amount of aromatic hydrocarbon such as benzene, toluene and xylene, halogenated hydrocarbon such as trichlene, ether such as propyl ether and isopropyl ether, etc. , Esters such as ethyl acetate and isopropyl acetate, alcohols such as ethanol and isopropanol, etc. are mixed, the boiling point is higher than the melting point of ε-caprolactam and lower than the boiling point of ε-caprolactam, preferably the boiling point is higher than the melting point of ε-caprolactam. And it can also be used as a mixed solvent of about 150 ° C. or lower.

  Among these solvents, a combination of solvents with low polarity and close boiling points is recommended. In this case, in continuous operation, even if there is a change in the solvent composition, the change in the solubility of lactam is small and the influence on the crystallization yield is small, so that the concentration control of the solvent becomes easy. As such a solvent combination, an aliphatic linear hydrocarbon and an alicyclic hydrocarbon are preferable, and a combination of n-heptane and cyclohexane is particularly preferable.

  Note that, without using the dissolution tank 1, for example, the crude lactam and the solvent may be mixed in a pipe and supplied to the crystallization tank 2 described later, and the crude lactam and the solvent may be supplied to the crystallization tank 2. It is good also as supplying each directly to the crystallization tank 2, without mixing before supplying to.

  The solution adjusted in the dissolution tank 1 is supplied to the crystallization tank 2. In the crystallization tank 2, the organic solvent in the solution is evaporated under reduced pressure to crystallize ε-caprolactam (evaporation crystallization), and a slurry in which ε-caprolactam is dispersed is obtained. In the evaporative crystallization, the crystallization tank as seen in the system in which the wall surface in contact with the solution in the crystallization tank 2 is cooled and crystallized by using the latent heat of vaporization of the organic solvent for cooling and crystallization. Scaling on the heat transfer surface 2 is suppressed, and high-quality ε-caprolactam can be obtained stably. The crystallization temperature is preferably about 20 ° C to 60 ° C.

  In the operation of evaporation crystallization, the slurry concentration can be stabilized by securing the time necessary for crystallization (that is, by having an aging time). The time for this is preferably 5 minutes or more. In order to extend the average residence time of the crystallization tank 2, it is necessary to increase the capacity of the crystallization tank 2, and an appropriate time is selected from the viewpoint of crystal quality and economy. The time necessary for crystallization is sufficient to be 5 minutes to 60 minutes, preferably 20 minutes to 40 minutes.

  The evaporation crystallization in the crystallization tank 2 may be performed in a continuous manner or in a batch manner (batch manner). Since production efficiency can be improved, it is preferable to carry out by a continuous type.

  The organic solvent evaporated in the crystallization tank 2 is supplied to the condenser 3. In the condenser 3, the organic solvent evaporated in the crystallization tank 2 is liquefied. The obtained organic solvent (hereinafter sometimes referred to as a circulating solvent) can be used as an organic solvent for dissolving the crude lactam in the dissolution tank 1 at least partially.

  In addition, in the crystallization tank 2, in addition to the organic solvent added to dissolve the crude lactam in the dissolution tank 1, it is assumed that low boiling point components (highly volatile impurities) contained in the crude lactam also evaporate. . In the condenser 3, such low-boiling components are also liquefied, but the circulating solvent obtained does not contain high-boiling components. Therefore, even if the circulating solvent is reused for dissolving the crude lactam, impurities (low boiling point components) due to the circulating solvent do not easily remain in the obtained ε-caprolactam, and can be suitably recycled. Further, when the concentration of the low boiling point component contained in the circulating solvent is sufficiently low so as not to affect the purity of ε-caprolactam, it can be used as an organic solvent for washing in the crystal washing machine 5 described later. is there.

  The slurry liquid in which crystals are precipitated and reach a predetermined slurry concentration is introduced into the solid-liquid separator 4. In the solid-liquid separator 4, the introduced slurry can be separated into a solid phase containing ε-caprolactam crystals and a liquid phase containing impurities by solid-liquid separation. The crystallization in the crystallization tank 2 and the solid-liquid separation in the solid-liquid separator 4 are preferably carried out continuously.

  Solid-liquid separation can be performed using a filter used for normal crystallization, such as vacuum filtration, pressure filtration, etc. In order to perform continuous filtration, centrifugal filtration, continuous scraping centrifugal A filter, a centrifugal decanter, or the like may be used. Especially in continuous scraping centrifugal filters and centrifugal decanters, crystals can be rinsed continuously, and the liquid phase containing impurities attached to the crystals can be washed to further improve the quality of the crystals. Is preferable.

  Crystals (solid phase) of ε-caprolactam separated by the solid-liquid separator 4 are supplied to a crystal washer 5 for washing the solid phase and washed using an organic solvent. Thereby, impurities adhering to the crystal surface can be removed, and ε-caprolactam (purified lactam) with higher purity can be obtained as compared with those not washed.

  The organic solvent used for the washing is preferably a solvent having a low solubility of ε-caprolactam, and the above-described hydrocarbon solvent having a low polarity can be used.

  In the present embodiment, the solid-liquid separator 4 and the crystal washer 5 are described as separate devices, but the same device functions as the solid-liquid separator 4 and the crystal washer 5. It is good also as having (a solid-liquid separator has a crystal washing part).

  The liquid phase containing the organic solvent separated by the solid-liquid separator 4 and the liquid phase containing the organic solvent discharged from the crystal washing machine 5 may be partially used as the organic solvent used in the dissolution tank 1. .

  In this case, a threshold value is set for the concentration of impurities contained in each liquid phase, and can be used as an organic solvent used in the dissolution tank 1 as long as the impurity concentration of each liquid phase does not exceed the threshold value. Then, it is preferable because the impurities removed by crystallization are not circulated unnecessarily in the previous treatment.

  Usually, the concentration of impurities contained in the liquid phase generated in the downstream crystal washing machine 5 is lower than the liquid phase generated in the solid-liquid separator 4. For this reason, when it is known in advance that the concentration of impurities in the liquid phase generated in the crystal washer 5 is always below the above threshold during steady operation, a part of the liquid phase generated in the crystal washer 5 is dissolved. It is preferable that the operating conditions are such that the liquid phase generated in the solid-liquid separator 4 is supplied to the subsequent crystallization tank 6 as an organic solvent used in the tank 1.

  Of course, if the impurity concentration contained in the liquid phase generated in the solid-liquid separator 4 is less than a preset threshold value, the liquid phase generated in the solid-liquid separator 4 may be circulated in the dissolution tank 1. If the impurity concentration of the liquid phase obtained by the crystal washer 5 is equal to or higher than the above threshold value, it is preferable to supply all of the impurities to the subsequent crystallization tank 6 without circulating them to the dissolution tank 1.

  More specifically, ε-caprolactam (purified lactam after treatment) is used so that the degree of treatment of the crude lactam in the first step is such that a basic compound such as cyclohexanone oxime, MTHI, or OHP is not more than a specific concentration in the crystallization stage. ) -Containing cyclohexanone oxime is less than 10 ppm relative to ε-caprolactam, 1,2,3,4,6,7,8,9-octahydrophenazine is less than 10 ppm, 3-N-methyl- It is preferable to analyze and manage the concentration of 4,5,6,7-tetrahydrobenzimidazole to be less than 25 ppm.

  The degree of treatment of the crude lactam in the first step is controlled by the impurity content index. The degree of removal of impurities by the crystallization treatment can be adjusted by crystallization conditions such as the type of solvent used, the amount of solvent, and the crystallization temperature, and may be confirmed by preliminary experiments. The crystallization treatment may usually be performed once, but may be performed a plurality of times, and a plurality of crystallization treatments are particularly recommended for a crude lactam having a large amount of impurities. For caprenolactams that are difficult to remove in the crystallization method, ε-caprolactam obtained by solid-liquid separation after crystallization treatment can be removed by contacting with hydrogen in the presence of a hydrogenation catalyst. Is possible. Such treatment can usually reduce caprenolactams to less than 25 ppm.

(Second step)
Among the liquid phases discharged from the solid-liquid separator 4 and the crystal washer 5, the liquid phase not used in the dissolution tank 1 is purified by combining known methods such as distillation, extraction, chemical treatment, activated carbon treatment, etc. However, the yield can be easily increased by recovering the crystals by recrystallizing the liquid phase. The recovered crystals can be efficiently recovered from the crude lactam by adopting a method of recycling the recovered crystals to the first step.

  More specifically, the liquid phase not used in the dissolution tank 1 is introduced into the crystallization tank 6. Various methods can be used for the crystallization method in the crystallization tank 6. For example, evaporation crystallization may be performed as in the first step. In addition, the remaining liquid phase is an aliphatic hydrocarbon solvent controlled at a low temperature or a mixed solvent of an aliphatic hydrocarbon solvent and a small amount of an organic solvent having higher polarity than the aliphatic hydrocarbon solvent at a low temperature. While mixing the controlled ones to crystallize the lactam, the generated heat of crystallization is offset by the sensible heat of the cold solvent and crystallized at a constant temperature to form a slurry mixture. Crystallization may be performed as growing.

  When evaporating crystallization is performed in the crystallization tank 6, it evaporates by providing a condenser (not shown) in the crystallization tank 6 in the same manner as the condenser 3 is provided in the crystallization tank 2. The organic solvent can be recovered and recycled as a solvent for dissolving the crude lactam in the dissolution tank 1 and an organic solvent for washing in the crystal washer 5.

  It is particularly effective from the viewpoint of energy saving to distill away the solvent to some extent using a multi-effect can etc. before evaporative crystallization.

  The slurry after the crystallization treatment is introduced into a solid-liquid separator 7 and separated into ε-caprolactam crystals (recovered lactam) as a solid phase and a liquid phase in which impurities are concentrated. The crystallization in the crystallization tank 6 and the solid-liquid separation in the solid-liquid separator 7 are preferably carried out continuously. Moreover, it is more preferable that the crystallization and solid-liquid separation in the first step and the crystallization and solid-liquid separation in the second step are both carried out continuously. The recovered lactam discharged from the solid-liquid separator 7 is introduced into the dissolution tank 1 and used as a raw material (crystallization raw material) in the first step.

  On the other hand, the liquid phase discharged from the solid-liquid separator 7 is distilled in a solvent recovery step (not shown) to recover the organic solvent and the impurities are separated as a residue. As a result, the concentrated impurities are discharged out of the system, avoiding the accumulation of impurities in the system, and enabling the long-term continuous operation of this manufacturing process.

  Note that, when mixed solvents having different boiling points are used, the composition of the recovered solvent is different. However, it is preferable to reuse the mixture after adjusting the concentration by mixing the recovered solvent including the solvent recovery step.

The recovered solvent may be circulated as a solvent used in the crystallization tank 2 and the like, and the discharge from this process is only the residue in the solvent recovery step, resulting in a manufacturing process with very little waste.
The method for producing ε-caprolactam according to this embodiment is performed as described above.

  According to the production method of ε-caprolactam as described above, by adopting evaporation crystallization in the crystallization tank 2, energy for operating a refrigerator or the like for cooling the crystallization tank 2 during crystallization is unnecessary. Therefore, impurities can be reduced with less energy consumption, and high-quality ε-caprolactam can be produced with good yield.

DESCRIPTION OF SYMBOLS 1 ... Dissolution tank, 2 ... Crystallization tank, 3 ... Condenser, 4 ... Solid-liquid separator, 5 ... Crystal washing machine, 6 ... Crystallization tank, 7 ... Solid-liquid separator

Claims (12)

From a solution of crude ε-caprolactam obtained by Beckmann rearrangement of cyclohexanone oxime in an organic solvent, the organic solvent was evaporated under reduced pressure to crystallize ε-caprolactam, and then the crystallized ε-caprolactam was A first step of solid-liquid separation from the solution;
A second step of further crystallizing ε-caprolactam from the liquid phase obtained by solid-liquid separation and solid-liquid separation of the crystallized ε-caprolactam from the liquid phase.   The method for producing ε-caprolactam according to claim 1, wherein at least a part of the organic solvent evaporated from the solution is recycled as an organic solvent for dissolving the crude ε-caprolactam.   The method for producing ε-caprolactam according to claim 1 or 2, wherein ε-caprolactam obtained by solid-liquid separation in the second step is circulated as a crystallization raw material in the first step.   The organic solvent is recovered from the liquid phase obtained by solid-liquid separation in the second step, and at least a part of the recovered organic solvent is recycled as an organic solvent for dissolving the crude ε-caprolactam. 4. The method for producing ε-caprolactam according to any one of items 1 to 3.   The ε- according to any one of claims 1 to 4, wherein in at least one of the first step and the second step, the ε-caprolactam obtained by solid-liquid separation is washed with an organic solvent. A method for producing caprolactam.   The method for producing ε-caprolactam according to any one of claims 1 to 5, wherein crystallization and solid-liquid separation are continuously carried out in at least one of the first step and the second step.   The organic solvent for dissolving the crude ε-caprolactam is an aliphatic hydrocarbon solvent or a mixed solvent of an aliphatic hydrocarbon and a small amount of an organic solvent having a polarity higher than that of the aliphatic hydrocarbon. The manufacturing method of the epsilon caprolactam of any one.   The ε-caprolactam according to claim 7, wherein the aliphatic hydrocarbon solvent is at least one of an aliphatic straight chain hydrocarbon, an aliphatic side chain hydrocarbon, and an alicyclic hydrocarbon having 6 to 12 carbon atoms. Manufacturing method.   The method for producing ε-caprolactam according to any one of claims 7 and 8, wherein the aliphatic hydrocarbon solvent is a mixed solvent of an aliphatic linear hydrocarbon and an alicyclic hydrocarbon.   The method for producing ε-caprolactam according to any one of claims 1 to 9, wherein the crude ε-caprolactam is obtained by gas phase Beckmann rearrangement of cyclohexanone oxime in the presence of a solid catalyst.   11. The ε according to claim 1, wherein in the first step, ε-caprolactam obtained by solid-liquid separation after crystallization treatment is then contacted with hydrogen in the presence of a hydrogenation catalyst. -Method for producing caprolactam.   The concentration of cyclohexanone oxime contained in the crude ε-caprolactam is 10 ppm or more with respect to ε-caprolactam, and the concentration of 1,2,3,4,6,7,8,9-octahydrophenazine is with respect to ε-caprolactam. 10 ppm or more, the concentration of 3-N-methyl-4,5,6,7-tetrahydrobenzimidazole is 25 ppm or more with respect to ε-caprolactam and the concentration of caprenolactams is 25 ppm or more with respect to ε-caprolactam. The manufacturing method of the epsilon caprolactam of any one of Claim 1 to 11.

Images